Check out Level10 too. They can rebuild your existing for 1500-2000 or ship you a custom built 1 for 3500-4000 that can handle up to 650WHP.

anybody have any experience with the GTM built trannys?

Somethings not right. How are you "barely" faster than a stock C5? Are you talking about the base model or the Z06? Then again, it shouldn't even matter.
I've raced a couple of base C5s in my Turbo Talon A/T I had and beat them. Ran a C5 Z06 on roll and it beat me (didn't appear stock, but still). Your power curve can't be that that far off.
What's your definition of barely?

EDIT: Missed the end of page 4. I've looked at SFR's before, I've been debating between theirs and GTM's but I haven't heard any reviews on that tranny. Most likely I'll be going with GTM.

I'm referring to the base model, I haven't ran against a Z06 yet. I'm also not referring to a track where launches will determine the results. The term "barely" is saying the acceleration between the Vette and myself was almost equal. An LS engine doesn't have turbo lag or lose 130+ torque after 5K RPM.

I was quoted $525 at Stillen and this is including multiple maps. I'm planning to do one with standard 91 octane and another with 91 octane + VP MS109 (50/50 mix) to make 100 octane.

I'd highly recommend Church where most of the SoCal VQ's get tuned.